Re: [PATCH] Equivalence Class Filters

On 12/6/15 10:38 AM, Tom Lane wrote:
> I said "in most cases". You can find example cases to support almost any
> weird planner optimization no matter how expensive and single-purpose;
> but that is the wrong way to think about it. What you have to think about
> is average cases, and in particular, not putting a drag on planning time
> in cases where no benefit ensues. We're not committing any patches that
> give one uncommon case an 1100X speedup by penalizing every other query 10%,
> or even 1%; especially not when there may be other ways to fix it.

This is a problem that seriously hurts Postgres in data warehousing
applications. We can't keep ignoring optimizations that provide even as
little as 10% execution improvements for 10x worse planner performance,
because in a warehouse it's next to impossible for planning time to matter.

Obviously it'd be great if there was a fast, easy way to figure out
whether a query would be expensive enough to go the whole 9 yards on
planning it but at this point I suspect a simple GUC would be a big
improvement.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com